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Excerpt
James E. Sheedy, College of Optometry , The Ohio State University , Columbus, Ohio
This book was written based on lectures to optometry students at Aston University, Birmingham, UK. It is an uncomplicated and straightforward presentation on the topic of spectacle lenses. It is ideally written as a textbook for a course on spectacle lenses, or what is commonly called “ophthalmic optics” in most institutions. However, the book could also be useful as an educational tool for anyone working in the industry.
The first chapter provides a condensed, basic background in geometrical optics. It does not assume that the reader has any background in optics and quickly progresses from vergence to laws of refraction to surface and lens refraction to thin lenses, prism, thick lenses and mirrors. This whirlwind tour through geometrical optics is well organized and precise—but it could be a bit dizzying for a person with no background in the topic. However, geometrical optics is a prerequisite course for ophthalmic optics in most optometry schools; therefore, most students already have a background in geometric optics. It is probably not possible to write a book on spectacle lenses without first discussing geometrical optics—if for no other reason than to establish the author’s ground rules for symbol and sign convention.
The second chapter covers spherical lens forms and lens thickness. It also develops the topics of spectacle magnification, aniseikonic lenses, field of view through lenses, and lens effectivity. Consistent with the tenor of the book, these topics are covered tightly and accurately, although I might prefer that these particular topics be covered later in the book (course). The third and fourth chapters provide comprehensive discussions of toric lenses and prism, respectively. These chapters include practical applications such as prescription writing, transposition, clinical uses, PD, lens centering, and minimum blank size.
The remaining six chapters are less mathematical and provide good coverage of lens materials and lens manufacture, measurement methods and instruments, lens aberrations and best form lenses, aspheric lenses, multifocal lenses including progressive addition lenses, and tints and coatings. Each of these topical areas is broadly covered and provides the information needed for clinical application. They are not highly dependent on a complete understanding of geometrical optics, and, hence, can serve as stand-alone treatises for a reader with a primary interest in learning about the topic without necessarily understanding all of the optical principles.
As a whole, the book is well organized and succinct. I could nitpick a few items, but this review would be unbalanced if I chose to do so here. The figures in the earlier chapters applying to geometrical optics are not a strong point of the book. Some are a bit confusing. Some are technically accurate, but the drawing may have an obvious geometry flaw such as a line drawn through the center of surface curvature not appearing to be normal to the surface. Some figures have the refracting/reflecting surface oriented vertically, and others have it oriented horizontally. Although it could be argued that this has greater educational value, I feel that it is best to use the same orientation for students or readers who are exposed to the topic for the first time. Also, a few symbols are used in figures but not listed in the Glossary of Terms—thereby decreasing the effectiveness of the Glossary. The figures in the later chapters are very adequate to the task.
